In 1968 the Food and Nutrition Board (FNB) of the National Research Council (NRC) established a recommended dietary allowance (RDA) for folacin of 400 microgram/day for adults with an additional allowance of 400 microgram/day for the increased needs of pregnancy and lactation. This level was retained in the 1980 revision of the RDA. Only 25% of the folacin in common U.S. foods is generally throught to be nutritiionally available. The average American diet provides approximately 230 microgram of folacin per day which is approximately one half of the RDA. Given the above information widespread folacin deficiency in the American population would be expected. This deficiency, however, was not confirmed by a detailed and thoughtful review of the National Nutrition and Health Examination Survey (NHANES II) data which showed that only 6% or less of the population had blood folacin levels that were considered low. Although the RDAs are based on a comprehensive, in depth review of available scientific evidence, it is now clear that the FNB was handicapped in developing its RDAs because of inadequacies in measuring folacin content of foods, folacin intake, and folacin bioavailability and in correlating these measuring folacin content of foods, folacin intake, and folacin bioavailability and in correlating these measurements with clinical and/or epidemiologic evaluations of folacin status. These inadequacies persist largely because newly developed techniques of analytical, synthetic and structural chemistry have not been applied to the acquisition of fundamental compositional, bioavailability and nutritional status data for this vitamin. The reference and standard assay for folacin is still a microbiological assay| This proposal seeks to develop, validate and apply novel physico- chemical techniques of liquid chromatography in conjunction with mass spectrometry and stable isotopes to the above task. The information from these studies will provide reliable compositional data on America foods and will assess nutritional bioavailability of this important vitamin in human subjects. A variety of food items will be analyzed for folacin using isotope dilution mass spectrometry (IDMS) to accurately quantitfy individual folacin congener profiles for each food. Once reliable analytical methods are perfected, bioavailability will be measured in an animal model - rat - to establish the model's validity. The validated model will then be applied in human subjects in a subsequent proposal.